AVAILABILITY AND FIELD WATER-QUALITY OF GROUND WATER IN THE MARBURG SCHIST IN WEST MANHEIM TOWNSHIP, YORK COUNTY, PA

Current population growth of about 5 percent per year in West Manheim Township (Township) coupled with recent droughts has led Township officials to undertake an effort to evaluate the capability of the bedrock aquifers to meet future, water-resources needs. Availability of ground water in the Township is limited by the physical characteristics of the underlying bedrock and its upland topographic setting. The Marburg Schist, which underlies approximately 90 percent of the Township, is one of the lowest yielding aquifers in the Commonwealth. About 25 percent of the wells in the Marburg Schist have driller reported yields of 2 gallons per minute (gal/min) or less, and 50 percent of the wells have specific capacities of 0.09 (gal/min) per foot of drawdown or less, indicating borehole storage contributes significantly to driller reported yields. Driller reports also indicate water-producing zones are shallow and few in number. In general, 50 percent of the water-producing zones are penetrated by a depth of 87 ft and 90 percent by a depth of 183 ft. Nonparametric tests (Spearman) indicate strong inverse correlation between well depth and yield (-0.71) and well depth and specific capacity (-0.66). Field measurements of pH and specific conductance indicate that water in the Marburg Schist is slightly acidic and relatively low in dissolved solids. Approximately 50 percent of the wells sampled contained water with a pH less than the U.S. EPA secondary drinking water regulation of 6.50. Specific conductance ranged from 80 to 1,720 microsiemens per centimeter (uS/cm), the median was 187 uS/cm.